Internal heat exchanger

ABSTRACT

In an internal heat exchanger, when a corresponding diameter of a high pressure passage  5   a  is ψh, a passage length Lh of the high pressure passage ( 5   a ) is so set as to satisfy the relation 9.16/{LN(4.5 −ψh +1.03)}&lt;Lh&lt;46/{LN(4.5 −ψh +1.03)}, and when a corresponding diameter of a low pressure passage  5   c  is ψl, a passage length Ll of the low pressure passage  5   c  is so set as to satisfy the relation 9.16/{LN(0.56×6 −ψl +1.02)}&lt;Ll&lt;46/{LN(0.56×6 −ψ +1.02)}, a passage sectional area Ah of the high pressure passage  5   a  is so set as to satisfy the relation 100×(0.25×ψh 1.2 ) −1/(0.04×ψh+1.7) &lt;Ah &lt;100×(500×ψh 1.2 ) −1(0.04×ψh+1.7) , and a passage sectional area Al of the low pressure passage  5   c  is so set as to satisfy the relation 1.65/ψl 0.67 &lt;Al&lt;626/ψl 0.67 .

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention is applied to a vapor compression type refrigerator usingcarbon dioxide as a refrigerant, between internal heat exchangers, forconducting heat exchange between a high pressure side refrigerant and alow pressure side refrigerant.

2. Description of the Related Art

Most internal heat exchangers applied to vapor compression typerefrigerators are employed to perform heat exchange between a highpressure side refrigerant flowing into a pressure reduction device suchas an expansion valve and a low pressure refrigerant sucked into acompressor, to lower the temperature and enthalpy of the refrigerantflowing into the pressure reduction device and to improve arefrigeration capacity of the vapor compression type refrigerators byincreasing a heat absorption quantity in an evaporator, that is, arising amount of enthalpy in the evaporator.

When such an internal heat exchanger is used, the capacity of the vaporcompression type refrigerator can be improved. Because the number ofcomponents constituting the vapor compression type refrigeratorincreases in this case, the size of the internal heat exchanger must bereduced in order to mount a vapor compression type refrigerator havingthe internal heat exchanger into an air conditioner for a car having alimited mounting space.

When the size of the internal heat exchanger is merely reduced, the highpressure side refrigerant cannot sufficiently be cooled in the internalheat exchanger, and the refrigeration capacity of the vapor compressiontype refrigerator cannot sufficiently be improved.

SUMMARY OF THE INVENTION

In view of the problems described above, the invention is directed toprovide, in the first place, a novel internal heat exchanger differentfrom internal heat exchangers of the prior art and to provide, in thesecond place, an internal heat exchanger suitable for a vaporcompression type refrigerator using carbon dioxide as a refrigerant.

To accomplish these objects, a first aspect of the invention provides aninternal heat exchanger applied to a vapor compression type refrigeratorusing carbon dioxide as a refrigerant, having a high pressure passage (5a) through which a high pressure refrigerant flows and a low pressurepassage (5 c) through which a low pressure side refrigerant flows, andconducting heat exchange between the high pressure side refrigerant andthe low pressure side refrigerant while the flow of the high pressureside refrigerant and the flow of the low pressure side refrigerantconstitute counter-flows, wherein, when the length units are millimetersand a corresponding diameter of the high pressure passage (5 a) is ψh, apassage length (Lh) of the high pressure passage (5 a) is greater than9.16/{LN(4.5^(−ψh)+1.03)} and smaller than 46/{LN(4.5^(−ψh)+1.03)}, andwhen the length units are millimeters and a corresponding diameter ofthe low pressure passage (5 c) is ψl, a passage length (Ll) of the lowpressure passage (5 c) is greater than 9.16/{LN(0.56×6^(−ψl)+1.02)} andsmaller than 46/{LN(0.56×6^(−ψl)+1.02)}.

In consequence, a compact and high performance internal heat exchangercan be obtained as shown in later-appearing FIGS. 3 and 4.

According to another aspect of the invention, there is provided aninternal heat exchanger applied to a vapor compression type refrigeratorusing carbon dioxide as a refrigerant, having a high pressure passage (5a) through which a high pressure refrigerant flows and a low pressurepassage (5 c) through which a low pressure side refrigerant flows, andconducting heat exchange between the high pressure side refrigerant andthe low pressure side refrigerant while the flow of the high pressureside refrigerant and the flow of the low pressure side refrigerantconstitute counter-flows, wherein, when a length unit is millimeter anda corresponding diameter of the high pressure passage (5 a) is ψh, apassage sectional area (Ah) of the high pressure passage (5 a) isgreater than 100×(0.25×ψh^(1.2))^(−1/(0.04×ψh+1.7)) and smaller than100×(500×ψh^(1.2))^(−1/(0.04×ψh+1.7)), and when the length units aremillimeters and a corresponding diameter of the low pressure passage (5c) is ψl, a passage sectional area (Al) of the low pressure passage (5c) is greater than 1.65/ψl^(0.67) and smaller than 626/ψl^(0.67).

Inconsequence, a compact and high performance internal heat exchangercan be obtained as shown in later-appearing FIGS. 5 and 6.

According to the invention, both of both of the high pressure passageand the low pressure passage (5 c) are constituted by a plurality ofpassages, and wherein the number (Nh) of the high pressure passages (5a) is greater than 400/(π×ψh²)×(0.25×ψh^(1.2))^(−1/(0.04×ψh+1.7)) andsmaller than 400/(π×ψh²)×(500×ψh^(1.2))^(−1/(0.04×ψh+1.7)), and thenumber (Nl) of the low pressure passages (5 c) is greater than2.1/ψl^(2.47) and smaller than 797/ψl^(2.67).

According to the invention, further, the high pressure passage (5 a) andthe low pressure passage (5 c) are aligned on the same axis andconstitute a double tube structure.

According to the invention, further, the high pressure passage (5 a) andthe low pressure passage (5 c) are shaped into a flat shape.

The present invention may be more fully understood from the descriptionof preferred embodiments of the invention as set forth below togetherwith the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a schematic view of a vapor compression type refrigeratoraccording to an embodiment of the invention;

FIG. 2 is a schematic view of an internal heat exchanger according to afirst embodiment of the invention;

FIG. 3 is a graph showing the relation between heat exchange efficiencyQ and a passage length Lh of a high pressure passage 5 a in a highpressure tube 5 b when a passage sectional diameter ψ of the highpressure passage 5 a is used as a parameter;

FIG. 4 is a graph showing the relation between heat exchange efficiencyQ and a passage length Ll of a low pressure passage 5 c in a lowpressure tube 5 d when a passage sectional diameter ψ of the lowpressure passage 5 c is used as a parameter;

FIG. 5 is a graph showing the relation between a pressure loss ΔP/L perunit passage length and a passage sectional area Ah of the high pressurepassage 5 a in the high pressure tube 5 b when a passage sectionaldiameter ψ of the high pressure passage 5 a is used as a parameter;

FIG. 6 is a graph showing the relation between heat exchange efficiencyQ and a passage sectional area Al of the low pressure passage 5 c in thelow pressure tube 5 d when a passage sectional diameter ψ of the lowpressure passage 5 c is used as a parameter;

FIG. 7 is a schematic view of an internal heat exchanger according to asecond embodiment of the invention; and

FIG. 8 is a schematic view of an internal heat exchanger according to athird embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment

In this embodiment, an internal heat exchanger for a vapor compressiontype refrigerator according to the invention is applied to an airconditioner for a car using carbon dioxide as a refrigerant, and FIG. 1is a schematic view of the vapor compression type refrigerator accordingto the embodiment.

Referring to FIG. 1, a compressor 1 acquires power from an externaldriving source such as a driving source for a vehicle (e.g. internalcombustion engine such as an engine) and sucks and compresses arefrigerant. A radiator 2 is a high pressure side radiator that performsheat exchange between a high pressure refrigerant ejected from thecompressor 1 and external air and cools the high pressure refrigerant.

A pressure reduction device 3 reduces the pressure of the high pressureside refrigerant flowing out from the radiator 2. This embodiment uses adevice that equi-enthalpically reduces the pressure such as an expansionvalve or a fixed choke.

An evaporator 4 is a low pressure side heat exchanger that evaporates alow pressure side refrigerant the pressure of which is reduced by thepressure reduction device 3, performs heat exchange between the lowpressure side refrigerant and air blowing into a passenger compartmentand exhibits a cooling capacity by evaporating the low pressurerefrigerant.

Incidentally, this embodiment uses carbon dioxide as the refrigerant andthe critical temperature of carbon dioxide is as low as about 31° C.Therefore, the pressure of the high pressure side coolant, that is, thedischarge pressure of the compressor 1, is set to be higher than thecritical pressure of the refrigerant to secure a necessary heatradiation capacity (temperature difference). As the high pressure siderefrigerant has a pressure higher than the critical pressure, itsenthalpy is lowered by lowering the temperature without condensing thecoolant inside the radiator 2.

The internal heat exchanger 5 is a heat exchanger that performs heatexchange between the low pressure side refrigerant flowing out from theevaporator 4 and the high pressure side refrigerant flowing out from theradiator 2. The internal heat exchanger 5 includes a high pressure tube5 b having a plurality of high pressure passages 5 a through which thehigh pressure side refrigerant flows and a low pressure tube 5 d havinglow pressure passages 5 c through which the low pressure siderefrigerant flows, as shown in FIG. 2.

Both tubes 5 b and 5 d are shaped into a flat shape by applying anextrusion process or a drawing process to a metal material such as analuminum alloy, and both passages 5 a and 5 c are formed in therespective tubes 5 b and 5 d simultaneously with molding of the tubes 5b and 5 c.

Both tubes 5 b and 5 d are unified by bonding by brazing, etc, in such amanner as to bring the flat surfaces into mutual and close contact witheach other. Incidentally, the term “brazing” used hereby means a bondingtechnology that uses a brazing material or a solder without melting abase material as described in “Connection-Bonding Technology” (TokyoElectric University Press).

Incidentally, a bonding technology that uses a filler metal having amelting point of 450° C. or above is referred to as “brazing” and thefiller metal used is referred to as a “brazing material”. A bondingtechnology that uses a filler metal having a melting point of 450° C. orbelow is referred to “soldering” and the filler metal is referred to as“solder”.

In this embodiment, when a corresponding diameter of the high pressurepassage 5 a is ψh, the passage length Lh of the high pressure passage 5a is so set as to be greater than 9.16/{LN(4.5^(−ψh)+1.03)} and smallerthan 46/{LN(4.5^(−ψh)+1.03)}. When a corresponding diameter of the lowpressure passage 5 c is ψl, the passage length Ll of the low pressurepassage 5 c is so set as to be greater than 9.16/{LN(0.56×6^(−ψl)+1.02)}and smaller than 46/{LN(0.56×6^(−ψl)+1.02)}.

Furthermore, when the corresponding diameter of the high pressurepassage 5 a is ψh, the passage sectional area Ah of the high pressurepassage 5 a is so set as to be greater than100×(0.25×ψh^(1.2))^(−1(0.04×ψh+1.7)) and smaller than100×(500×ψh^(1.2))^(−1/(0.04×ψh+1.7)). When the corresponding diameterof the low pressure passage 5 c is ψl, the passage sectional area Al ofthe low pressure passage 5 c is so set as to be greater than1.65/ψh^(0.67) and smaller than 626/ψl^(0.67). The units of length aremillimeters.

Here, the term “corresponding diameter” means the value obtained bymultiplying by 4 the sum of the passage sectional areas of the passages5 a, 5 c and dividing the product by the sum of the circumferences ofthe passages 5 a, 5 c corresponding to the length of a wetted perimeter.When each of the passages 5 a and 5 c is only one, the passage sectionalarea of one passage is multiplied by 4 and the product is then dividedby the circumference corresponding to the length of the wettedperimeter.

The symbol “LN” is the abbreviation of “Natural Logarithm” as is wellknown in the art and is a logarithm using e (=2.71828 . . . ) as thebase. Therefore, LN10, for example, means log.10.

Next, the features of the internal heat exchanger 5 according to theembodiment will be described.

FIG. 3 shows a numerical value simulation result representing therelation between heat exchange efficiency Q and the passage length Lh ofthe high pressure passage 5 a in the high pressure tube 5 b when thepassage sectional diameter ψ of the high pressure passage 5 a is used asa parameter and FIG. 4 shows a numerical value simulation resultrepresenting the relation between heat exchange efficiency Q and thepassage length Ll of the low pressure passage 5 c in the low pressuretube 5 d when the passage sectional diameter ψ of the low pressurepassage 5 c is used as a parameter.

The graph shown in FIG. 3 is numerically formulated as follows:Q=1−(1/4.5^(ψh)+1.03)^(−Lh/10).

When this equation is modified as to Lh:Lh=10·LN{1/(1−Q)}/LN{1/4.5^(ψh)+1.03}

The graph shown in FIG. 4 is numerically formulated as follows:Q=1−(0.56/6^(ψl)+1.02)^(−Ll/10).

When this equation is modified as to Ll:Ll=10·LN{1/(1−Q)}/LN{0.56/6^(ψl)+1.02}

In order to let the internal heat exchanger 5 operate as means forimproving the capacity of the vapor compression type refrigerator, heatexchange efficiency Q of at least 0.6 is required.

As can be obviously understood from FIGS. 3 and 4, on the other hand,heat exchange efficiency Q substantially gets into saturation at 0.99and can hardly be improved any longer. Therefore, heat exchangeefficiency is preferably a value that is greater than 0.6 and smallerthan 0.99.

Therefore, the upper limit values and the lower limit values of thepassage length Lh of the high pressure passage 5 a and the passagelength Ll of the low pressure passage 5 c are determined in thefollowing way on the basis of the equations given above:9.16/{LN(4.5^(−ψh)+1.03)}<Lh< 46/{LN(4.5^(−ψh)+1.03)}9.16/{LN(0.56×6^(−ψl)+1.02)}<Ll<46/{LN(0.56×6^(−ψl)+1.02)}

Therefore, a compact and high performance internal heat exchange 5 canbe obtained by so setting the passage length Lh of the high pressurepassage 5 a as to be greater than 9.16/{LN(4.5^(−ψh)+1.03)} and smallerthan 46/{LN(4.5^(−ψh)+1.03)} when the corresponding diameter of the highpressure passage 5 a is ψh, and by so setting the passage length Ll ofthe low pressure passage 5 c as to be greater than9.16/{LN(0.56×6^(−ψl)+1.02)} and smaller than 46/{LN(0.56×6^(−ψl)+1.02)}when the corresponding diameter of the low pressure passage 5 c is ψl.

When the passage sectional area of each passage 5 a and 5 c increases,the pressure loss occurring inside the passage 5 a and 5 c becomessmall, so that the velocity of the refrigerant flowing through eachpassage 5 a and 5 c increases and a heat transfer rate increases, too.

When the passage length of each passage 5 a and 5 c gets elongated, thecontact area between the high pressure tube 5 b and the low pressuretube 5 d, that is, the heat exchange area, increases. Consequently, whenthe passage length of each passage 5 a and 5 c increases, the pressureloss occurring in each passage 5 a and 5 c increases though the heatexchange quantity between the high pressure side refrigerant and the lowpressure side refrigerant increases. As a result, the velocity of therefrigerant flowing through each passage 5 a and 5 c drops and the heattransfer rate as well as heat exchange efficiency Q drop.

FIG. 5 shows a numerical value simulation result representing therelation between a pressure loss ΔP/L per unit passage length and thepassage sectional area Ah of the high pressure passage 5 a in the highpressure tube 5 b when the passage sectional diameter ψ of the highpressure passage 5 a is used as a parameter and FIG. 6 shows a numericalvalue simulation result representing the relation between heat exchangeefficiency Q and the passage sectional area Al of the low pressurepassage 5 c in the low pressure tube 5 d when the passage sectionaldiameter ψ of the low pressure passage 5 c is used as a parameter.

The graph shown in FIG. 5 is numerically formulated as follows:ΔPh/Lh=0.02×ψh ^(−1.2)×(100/Ah)^(0.04×ψh+1.7)

The graph shown in FIG. 6 is numerically formulated as follows:ΔPl/Ll=0.18×ψl ^(−1.3)×(100/Al)^(1.95)

Here, to satisfy the requirement for the vapor compression typerefrigerator, the pressure loss occurring in the internal heat exchanger5 must be less than 1,000 kPa. As can be obviously seen from FIGS. 5 and6, the pressure loss hardly changes with respect to the increase of thepassage sectional area when the pressure loss per unit passage length is0.005 kPa/mm or less. To reduce the size of the internal heat exchanger5, therefore, the pressure loss per unit passage length is preferablygreater than 0.1 kPa/mm.

Therefore, the upper limit values and the lower limit values of thepassage sectional area Ah of the high pressure passage 5 a and thepassage sectional area Al of the low pressure passage 5 c are determinedin the following way:100×(0.25×ψh ^(1.2) )^(−1/(0.04×ψh+1.7)) <Ah<100×(500×ψh^(1.2))^(−1/(0.04×ψh+1.7))1.65/ψl ^(0.67) <Al<626/ψl ^(0.67)

Therefore, a compact and high performance internal heat exchange 5 canbe reliably obtained by so setting the passage sectional area Ah of thehigh pressure passage 5 a as to be greater than 100×(0.25×ψh^(1.2))^(−1/(0.04×ψh+1.7)) and smaller than 100×(500ψh^(1.2))^(−1/(0.04×ψh+1.7)) and by so setting the passage sectional area Al ofthe low pressure passage 5 c as to be greater than 1.65/ψl^(0.67) andsmaller than 626/ψl^(0.67).

In this embodiment, the passages 5 a and 5 c have a circular sectionalshape and a plurality of passages 5 a and 5 c exist. Therefore, thenumber Nh of the high pressure passages 5 a and the number Nl of the lowpressure passages 5 c are given as follows:400/(π×ψh ²)×(0.25×ψh ^(1.2))^(−1/(0.04×ψh+1.7)) <Nh<400/(π×ψh²)×(500×ψh ^(1.2))^(−1/(0.04×ψh+1.7))2.1/ψl ^(2.67) <Nl<797/ψl ^(2.67)

As the number Nh of the high pressure passages 5 a and the number Nl ofthe low pressure passages 5 c are the natural numbers, the valuesobtained by counting fractions are used as the lower limit values of thenumbers Nh and Nl and those obtained by omitting the fractions are usedas the upper limit values of Nh and Nl.

Second Embodiment

In the first embodiment, the high pressure tube 5 b and the low pressuretube 5 d are unified by brazing, etc, but in this embodiment, the highpressure tube 5 b and the low pressure tube 5 d are integrally molded bythe extrusion process or the drawing process as shown in FIG. 7.

Third Embodiment

In the embodiments given above, the flat tubes constitute the internalheat exchanger. In this embodiment, however, the high pressure passage 5a and the low pressure passages 5 c are aligned on the same axis to forma double wall structure as shown in FIG. 8.

Incidentally, as the high pressure passage 5 a is only one in thisembodiment, the passage sectional area Ah is the passage sectional areaof one high pressure passage 5 a and the passage sectional area Al ofthe low pressure passages 5 c is the sum of a plurality of low pressurepassages 5 c.

Though the high pressure passage 5 a is arranged inside the low pressurepassages 5 c in this embodiment, the embodiment is not limited to thisconstruction and the high pressure passages 5 a may be arranged outsidethe low pressure passage 5 c.

Though the invention is applied to the air conditioner for a car in theembodiments described above, the application of the invention is notlimited thereto.

The construction of the internal heat exchanger 5 according to theinvention is not limited to those described in the foregoingembodiments.

In the internal heat exchanger 5 according to the invention, both highpressure passage 5 a and low pressure passage 5 c extend linearly butthe invention is not limited thereto. For examples, both passages 5 aand 5 c may well extend in a zigzag form.

While the invention has been described by reference to specificembodiments chosen for the purposes of illustration, it should beapparent that numerous modifications could be made thereto by thoseskilled in the art without departing from the basic concept and scope ofthe invention.

1. An internal heat exchanger applied to a vapor compression typerefrigerator using carbon dioxide as a refrigerant, having a highpressure passage (5 a) through which a high pressure refrigerant flowsand a low pressure passage (5 c) through which a low pressure siderefrigerant flows, and conducting heat exchange between said highpressure side refrigerant and said low pressure side refrigerant whilethe flow of said high pressure side refrigerant and the flow of said lowpressure side refrigerant constitute counter-flows, wherein: when thelength units are millimeters and a corresponding diameter of said highpressure passage (5 a) is ψh, a passage length (Lh) of said highpressure passage (5 a) is greater than 9.16/{LN(4.5^(−ψh)+1.03)} andsmaller than 46/{LN(4.5^(−ψh)+1.03)}, and when a length unit ismillimeter and a corresponding diameter of said low pressure passage (5c) is ψl, a passage length (Ll) of said low pressure passage (5 c) isgreater than 9.16/{LN(0.56×6^(−ψl)+1.02)} and smaller than46/{LN(0.56×6^(−ψl)+1.02)}.
 2. An internal heat exchanger according toclaim 1, wherein said high pressure passage (5 a) and said low pressurepassage (5 c) are aligned on the same axis and constitute a double tubestructure.
 3. An internal heat exchanger according to claim 1, whereintubular members constituting said high pressure passage (5 a) and saidlow pressure passage (5 c) are shaped into a flat shape.
 4. An internalheat exchanger applied to a vapor compression type refrigerator usingcarbon dioxide as a refrigerant, having a high pressure passage (5 a)through which a high pressure refrigerant flows and a low pressurepassage (5 c) through which a low pressure side refrigerant flows, andconducting heat exchange between said high pressure side refrigerant andsaid low pressure side refrigerant while the flow of said high pressureside refrigerant and the flow of said low pressure side refrigerantconstitute counter-flows, wherein: when the length units are millimetersand a corresponding diameter of said high pressure passage (5 a) is ψh,a passage sectional area (Ah) of said high pressure passage (5 a) isgreater than 100×(0.25×ψh ^(1.2))^(−1/(0.04×ψh+1.7)) and smaller than100×(500×ψh ^(1.2))^(−1/(0.04×ψh+1.7)), and when a length unit ismillimeter and a corresponding diameter of said low pressure passage (5c) is ψl, a passage sectional area (Al) of said low pressure passage (5c) is greater than 1.65/ψl^(0.67) and smaller than 626/ψl^(0.67).
 5. Aninternal heat exchanger according to claim 4, wherein both of said highpressure passage and said low pressure passage (5 c) are constituted bya plurality of passages, and wherein the number (Nh) of said highpressure passages (5 a) is greater than400/(π×ψh²)×(0.25×ψh^(1.2))^(−1/(0.04×ψh+1.7)) and smaller than400/(π×ψh²)×(500×ψh^(1.2))^(−1/(0.04×ψh+1.7)), and the number (Nl) ofsaid low pressure passages (5 c) is greater than 2.1/ψl^(2.67) andsmaller than 797/ψl^(2.67).
 6. An internal heat exchanger according toclaim 4, wherein said high pressure passage (5 a) and said low pressurepassage (5 c) are aligned on the same axis and constitute a double tubestructure.
 7. An internal heat exchanger according to claim 4, whereintubular members constituting said high pressure passage (5 a) and saidlow pressure passage (5 c) are shaped into a flat shape.